The CanOpener App and the Problem of Headphone Listening

It’s an old recording adage: Never mix on headphones. When I started engineering Damon & Naomi records, I learned why firsthand—what sounds great mixed on headphones sounds totally different (i.e., terrible) when played back on speakers. It’s the kind of mistake you don’t make twice. (I believe mine is out in the world somewhere on 7”, but I’ve done my best to forget the details.)

The reason for that difference is crossfeed, or the bleeding of one channel into another. Headphones, with their pure separation of left and right, have no crossfeed, but speakers, no matter how they are positioned in a room, always have some. And the classic "ideal" placement for stereo sound (an equilateral triangle between the listener and the two speakers) has a lot. Anticipating bleed between left and right, and using it to advantage, is a crucial part of stereo mixing and mastering.

And yet, earbuds have sprouted from our heads like mushrooms. These days we're all wearing headphones.

That makes for a massive mismatch between the production and consumption of music, but a new iPhone app called CanOpener ("cans" are British/muso slang for headphones) presents an ingenious solution. Using a deliberate crossfeed between left and right channels, together with a secret sauce of signal processing (drawing, in part, from innovations in gaming’s drive toward 3-D audio, and film’s toward surround sound), CanOpener conjures speakers from your headphones. Sound migrates from the sides of your head toward the front. And the feeling of a soundstage—a specific space before you, from which the music emanates—is restored.

For a listener like me, whose prized teen possession was a turntable with a smoked plastic dustcover, CanOpener makes music on headphones sound more "realistic" because I feel I can better locate where it comes from. In a New Yorker profile of astrophysicist Edgar Choueiri, who has recently turned his attention to 3-D audio design, Adam Gopnik explained, "In the real world, when you move your head, the sound signals change a little, and the brain knows where the sounds are coming from. That doesn’t happen with headphones, so the mind decides that the sound source can’t be 'out there.' Instead, as Choueiri says, 'the sound image collapses into your head.'"

Of course the idea of "headspace" is as much an artifact of the 1960s and 70s as wood-grained hi-fi systems. Alongside the triangle of speakers and listener, there’s that other classic listening set-up: door closed, windows open, headphones on. It's true (fifty million stoners can't be wrong) that lots of music mixed for stereo speakers does sound awesome on headphones. Audio engineers make frequent use of headphones for much the same reason: Listening for details (in the studio, that often translates to listening for flaws) is often most effective on headphones, because they eliminate a number of variables between the signal and your ears. Chief among those is the room you find yourself in.

Eliminating the environment from one’s listening also eliminates the soundstage created by a stereo mix, however. Headphones, for all their clarity and detail, leave a blank in the middle of our foreheads. As a member of the Institute of Electrical and Electronics Engineers puts it: "There are large errors in sound position perception associated with headphones, especially for the most important visual direction, out in front…it is very difficult to externalize sounds and avoid the inside-the-head sensation."

In other words, headspace is internal. This may be precisely the attraction when it comes to *Dark Side of the Moon—*and it’s probably no coincidence that the album dates from the formative years for the people who invented and marketed the iPod. Earbuds have the power to transform the whole world into the deep internal space of a teenage bedroom.

If it’s reproduction of sound in the external world you're after, that’s a different story. It also introduces a different problem, because whose external world are you are talking about? The paths to inner space may well be shared, as both meditation and Pink Floyd seem to demonstrate. But no two people are so close that they share the same spot on the earth. And our sense of location via hearing is so acute, we adjust it with every swivel of the head.

Which brings us back to the realism I find listening to music via CanOpener. To me, the imaginary space of a soundstage has always felt "real" because it places the listener in the audience at a performance. But that’s not the only way music happens in the external world; it’s just what was considered typical—and reproducible by the technology at the time—when my musical tastes and habits were formed. I can well imagine that a soundstage might seem less realistic than 3-D, surround sound, or even the harsh left/right divide of headphones to those whose listening began at a different moment on the tech spectrum—and with a different idea of the line between observer and participant. Gaming, POV video, and social media may have done more to smash the fourth wall of the soundstage than earbuds.

At the very least CanOpener is a must have for the still-analog set, those graying heads who show up at the record store every release day of the Dylan Bootleg Series. And I recommended it highly to anyone else interested in hearing more, via headphones, of what mixing and mastering engineers hear in the studio.

Plus, it has a mono button. Because once upon a time, stereo didn’t seem so realistic either.